Ellipsoidal reflector-building one

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I'm thinking of building myself an ellipsodial reflector to my upcoming 7" project. It will use the familar ellipse (in cartesian coordinates x^2/a^2+y^2/b^2=1 where a,b is the half axles) that is rotated and then cut by two planes(perpendicular) to achive something like this image.
So it's basically a ellipsoidal reflector cut in half but with a shade around it so it can be assembled together with bolts or dot welded together. The idea is that this will be done in practice with the use of a english wheel
pwrwhlngmachnes.jpg

I'm not really sure if will be able to do it, and if it actually will be impossible to make to similar shapes. The material I was thinking of is either aluminum or polished stainless steel. I have seen some great results with this wheel that is used to make car chassie details. The question is if it's even worth the job, but then on the other side could it be fun to see how it would turn out. This is btw my first post, been reading some but i can't really find if there is any good MH lamp/ballast distributers in europe?

/Gilgamesh
 
Most excellent.

I'm playing with something similar but in 1/3s. This would avoid any dark line from the joint. It is easier for the eye to notice if is simetric - left/right or up/down. going at an angle through the lcd would be harder to spot.

Is that you with the rolling press? Then you have access to a shop. You can also consider spinning one piece steel with spreading press wheels from inside. Must have supports outside so it wont buckle/deform.

fun stuff :smash:
........... :hypno2:
 
Oh my no it's not me, just a pic from internet;) I'm quite a bit younger than that :cool: To make it in one piece will probaly be very hard, i'm considering mayby to make it like you said out of more bits, but it depends on how hard it will be to make them look about the same!
I got access to a metal sheet workshop due to my father, the only problem is that i'm at uni now ---- 1300km from him but i'll be going home at easter so i hope it will be time to assemble my projector then, if i got all the parts that is. I'm thinking of building the chassie it of polished stainless steel, it will look just like it is chromed then, and put in some red LEDs for fan holes etc.
 
reflectivity

Even the very best stainless steel is only 65% reflective. Polished aluminum can get up over 90%. I think that dictates your choice of materials, unless you want to pay for silver plating the stainless!

I was thinking of trying this with at least four pieces. I would make a stamping mold, so I could make many identical pieces. Then just bolt them together.

BTW: You don't need to plot the equation to draw an ellipse. Just mark the two focal points on your template material. Put a little nail or pin at each point. Cut a piece of string or wire that is larger than two times the distance between the two focal points, and tie it in a loop. Put the loop of string over the pins, and then use it to guide a pencil as you draw the maximum-sized shape all the way around. That is a perfect ellipse. You can vary the width of the ellipse to match a condensor fresnel by making the loop longer or shorter.
 
Yes, aluminum or coated steel works. Not being a machinist i would find aluminum harder - requires more skill i think to keep an acurate shape with soft material. Steel is more resilient and puts up with my level of machining skill.

One note on the lip- I dont have a lip all the way around. When joined they leave a small gap (radius of bend) unless you weld and grind. Consider grinding the edge like a knife chamfer and overlap. The joint will be smaller i think.
 
diyAudio Member
Joined 2003
BTW: You don't need to plot the equation to draw an ellipse. Just mark the two focal points on your template material. Put a little nail or pin at each point. Cut a piece of string or wire that is larger than two times the distance between the two focal points, and tie it in a loop. Put the loop of string over the pins, and then use it to guide a pencil as you draw the maximum-sized shape all the way around. That is a perfect ellipse. You can vary the width of the ellipse to match a condensor fresnel by making the loop longer or shorter.

Why not just use Cad or Light Tools ;)

Trev:)
 
MH light distributor

This is btw my first post, been reading some but i can't really find if there is any good MH lamp/ballast distributers in europe?

I'm looking for a light distributor myself. I know of one in germany http://www.gadaffy.ch.vu/ and I think I'll order from there. It is a DIY projector store, so it has optics and other stuff too but it would be good to compare with other sources.
 
That seems like a decent place. I got some extra costs when i ordered from hongkong from ups, so right now was it almost as expensive as ordering it from a store in sweden.:( So my project will be a tad more expensive than i thought it would. I'm probaly going to use the 150W setup with the ballast. Does anyone know anywhere else to order ballasts in europe? I saw 150W ballasts @ebay with ignitor for around 36€+shipping.
 
Update

*Update*
I am now home and after some research did I give up the idea with building a good reflector out of segmented aluminum pieces. There is just too small angels and too hard to make it right. So this is what I did:
I went to my old gymnasium where i got a hold of a guy who can cnc mill it for me. I do not know the cost, but he seems like a nice guy;) . It will be in massive aluminium, but i doubt it will be very heavy. The next step in the procedure is to polish it, and that will be done in a lathe. I'll be back after the easter with some more info!
 
Holy CRAP! Well, I guess it depends on how big of a reflector you're talking about here. But in any case, that looks like a LOT of metal to remove. You'll start with a huge solid chunk of aluminum, then cut away most of it....

It doesn't matter how nice the guy is, unless he's doing it for free, it'll be in the hundreds.

There is much quicker and more economical way of creating hollowed rotated volumes. It's called metal spinning. What you do is place a big circular sheet of aluminum on the lathe, then chuck smooth or wheeled tools in the holder and start pushing the disc into the shape you need. Just compare to a profile cut out of cardboard or plywood as you go. Then, without removing the reflector from the lathe, you can polish it as it spins.
 
Yes I am aware of that technique but It is unfortuantly not an option availible to me here, nor do I have the skills to do it. The aluminium will be cut out from an 80mm(~3.92") axle and it will be around 70-80mm long so it won't be extremly expensive I hope. The piece will weight around 1kg not worked and that maybe equals 30$, I hope:D You can sell the aluminium that gets over to a decent price as well:cool:
 
Well, it shouldn't be too bad at that size. It depends on the alloy and treatment grade of the aluminum, too...some of that stuff can be difficult to chew through.

For that size of a reflector, casting could be a good option. Use the CNC mill to cut a form out of a wax cylinder, then use it for a lost-wax mold.
 
Only problem with that idea is that it will be hard to cool and heat up the lamp which reduces lamp life.
The wax idea i assume might work, but when i got access to a cnc mill will this be the easiest way to do it, and most likely the one with higest accuracy. Note: he will only mill out the inner ellipsodial form and leave the outside as an cylinder. Only a shame that i still loose a lot of light due to the 16:9 lilliput screen.

Cheers! Time to go to the sports cabin and drink some beer, bath some sauna, jacuzzi and something called bath barrell(big barrel with water thats warmed up and then you sit outside in the snow) I'll be back on monday/tuesday with some results if i'm lucky.
 
heating and cooling

Yes, heat can be a problem with these reflectors. I think you would need to make the hole for the lamp large enough for some cooling air to be pulled over the lamp surface and out the space around the base of the lamp. But you will also have to do something to remove IR from the light. Aluminum reflects IR just as well as it reflects visible light. With an eliptical reflector, you can use a very small dichroic mirror right at the second focal point. Very nice.

>bath barrell(big barrel with water thats warmed up and then you sit outside in the snow

I used to love doing that after skiing: Sit in a jacuzzi or hot tub (that's what we call a bath barrell) until you get too hot. Then sit in the snow or go in the unheated pool (with the icebergs!) for a while. Repeat as needed. I also did the same thing at a hot spring right next to an ice-cold mountain stream.

Lots of hot water is the ultimate sign of civilization.
 
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